What is optical SETI?

SETI (the Search for ExtraTerrestrial Intelligence) aims to detect signals from potential technical civilizations elsewhere in our galaxy (the Milky Way), which comprises some 400 billion stars^* in a flattened disk of some 100,000 light-years in diameter. Although it was once believed that planets, and particularly ones that could support life, were rare, we now know that most stars host planetary systems; and perhaps as many as 25% of stars have habitable planets -- thus some 100 billion potential sites for life in our galaxy alone!

From everything we know, the best way to signal over interstellar distances is with electromagnetic waves, which inhabit the familiar spectrum from radio, through microwave, infrared, visible light, and on up through x-rays and gamma rays. Electromagnetic radiation passes relatively unhindered through the galaxy, it goes at the speed of light, and it is easily generated and detected. For various reasons the optimum portions of the spectrum that can be explored for SETI are in the microwave (i.e., radio) or in the visible/infrared.

SETI beginnings, from Marconi onward, have taken place primarily in the radio-wave portion of the spectrum (i.e., searching for signals from an alien transmitter). But more recently, encouraged by Charles Townes (Nobel winner for the invention of the laser) and others, scientists have begun to look for optical signals (i.e., signals from an alien laser).

And here is a surprising fact: a laser of the sort that has already been available on Earth for several decades, when coupled with a large contemporary telescope, would be detectible by a sister telescope situated on a planet around any of the millions of stars within a thousand light-years distant to which it is aimed. When all relevant factors are taken into account, optical SETI is comparable to radio SETI in terms of communication efficiency. Of course, ultimately the best choice for a SETI wavelength is the one that They are using; this we can only guess, based on the science and technology of communication. Since Optical SETI (OSETI) seems fully practicable, we are launching a comprehensive search for possible laser communication from another civilization.

* And the milky way is one of some trillion galaxies in the known universe!

Why Panoramic?

Consider this: if we look only occasionally at any given star, and if they also transmit only intermittently in our direction, the chances of detection are small (this can be made quantitative). Following a suggestion by Jill Tarter, we have designed a system of many telescopes, pointing all over the sky, to approximate an "all-sky, all-the-time" search. Each telescope covers a 10° by 10° patch of sky, with a thousand sensitive and fast (nanosecond-speed) detectors, seeking the elusive flash that would change forever the way Earth sees its place in the universe.